Optic cavitation with CW lasers: A review

Abstract

The most common method to generate optic cavitation involves the focusing of short-pulsed lasers in a transparent liquid media. In this work, we review a novel method of optic cavitation that uses low power CW lasers incident in highly absorbing liquids. This novel method of cavitation is called thermocavitation. Light absorbed heats up the liquid beyond its boiling temperature (spinodal limit) in a time span of microseconds to milliseconds (depending on the optical intensity). Once the liquid is heated up to its spinodal limit (∼300 °C for pure water), the superheated water becomes unstable to random density fluctuations and an explosive phase transition to vapor takes place producing a fast-expanding vapor bubble. Eventually, the bubble collapses emitting a strong shock-wave. The bubble is always attached to the surface taking a semi-spherical shape, in contrast to that produced by pulsed lasers in transparent liquids, where the bubble is produced at the focal point. Using high speed video (105 frames/s), we study the bubble’s dynamic behavior. Finally, we show that heat diffusion determines the water superheated volume and, therefore, the amplitude of the shock wave. A full experimental characterization of thermocavitation is described.

Microbubble Generation with Tapered Optical Fibers

“…The physical origin of microbubbleformation is due to thermocavitation phenomena, which are basedon lightabsorption bya high-absorbing solution at the operating wavelengthof a laser source [6][7][8][9]. Although there are several means for inducing thermocavitation, the use of CW lasers has become very attractive due to its experimental simplicity and low cost [10].…”

Controllable generation and manipulation of micro-bubbles in water with absorptive colloid particles by CW laser radiation

“…In principle, each particle in the considered suspension is a separate heating source and serves as a center of bubble nucleation in which both the water vapor and the air gases dissolved in the water play important roles [2,21]. However, because of statistical fluctuations, the nucleation starts as a random event [19,20], and most probably occurs when the local conditions are especially favorable, e.g. when due to Brownian motion two or more particles appear anomalously close to each other and cause the local "excess" of released energy.…”

“…According to the known ideas [2,[19][20][21], the bubble nucleation initially occurs near a single absorbing nanoparticle in conditions of water superheating when the local temperature exceeds the standard boiling temperature 100 °C. Therefore, the theoretical superheating limit -critical conditions for water T C = 374 °C at pressure P C = 22.09 MPa -normally is not realized, and the new phase (bubbles), due to the presence of liquid-solid interfaces, adsorbed gas molecules and other imperfections, appear at lower temperatures, about T g = 200 °C [2,21].…”

“…However, the bubble generation by CW laser radiation is more suitable for various technological purposes. In this case, a rich and intricate dynamic behavior with fluid superheating and explosive bubble formation is possible [18][19][20], but more attractive is the availability of near-stationary regimes of bubble evolution permitting their detailed investigation and control [2,21]. It is the near-stationary long-living bubbles that provide exclusive possibilities for the precise mass transfer, highly selective chemical actions, targeted transport of biological cells and species, creation of adjustable microoptical systems, etc [3,4,6,[8][9][10][11][12][13].…”

A Comparison of Drug Delivery into Skin Using Topical Solutions, Needle Injections and Jet Injections

“…16,17 From the different energy sources used to power NFIs, a recent example is based on continuous wave (CW) lasers that cause a phenomenon known as thermocavitation to create liquid jets by heating the injectate above its boiling point with an explosive phase transition. 8,9,27,28,35 This work evaluates a CW-based needle-free micro-jet injector as a possible transdermal delivery alternative with minimal damage to the skin structure. For the purpose of this study, the topical solution delivery will be primarily associated with diffusion processes.…”